The invention relates to cleaners for conveyor belts and, more particularly, to a mount for a cleaning blade for scraping a conveyor belt clean.
Cleaners for conveyors that utilize a scraping element to remove debris and other materials from conveyor belts are well known. These conveyor belts often include metallic splices extending across the belt that run past the scraper blades during conveyor belt operations. The scraper blades are typically biased into engagement with the belt to allow them to resiliently shift away from the belt when surface irregularities on the belt are encountered such as due to the aforementioned metallic splices.
Generally, the goal of keeping the scraper blade in substantially constant contact with the belt to improve cleaning thereof is in competition with the need to allow the blades to shift away from the belt to avoid taking the full brunt of impacts with metallic splices and the like which can cause the scraper blades to rapidly wear. In heavier duty applications, this problem can be exacerbated by the use of thicker, more robust fasteners which create higher impact loads on the cleaning blade.
Another problem for keeping the blade in contact with the belt is its angle of attack relative to the belt. Generally, scalping angles where the blade leans forwardly or in the upstream direction as the belt travels downstream so as to form an obtuse angle with the belt surface upstream therefrom presents the most problems. With this aggressive angling of the blade, it will receive relatively high impact forces when encountering the splices or other carry-back materials on the belt. Also, these high impact forces can cause the blade to vibrate or xe2x80x9cchatterxe2x80x9d along the belt surface rather than staying in conformance with the belt reducing the cleaning efficiency of the blade. Catastrophic failure of the cleaner blade mounting components utilizing scalping angles is also of greater concern. Similarly, while a cleaning blade extending normal or vertically with respect to the belt surface to be cleaned is more desirable for cleaning, cleaning systems employing blade mounting members that only provide for vertical blade movements still can create high impact forces, particularly on belt splices which can cause excessive wear and ultimate failure of the splices.
By contrast, having the blade extending in the downstream direction so that it forms an acute angle with the belt surface upstream therefrom reduces the impact loading on the blade but can also create difficulties in keeping the blade in conformance with the belt surface. Unless the blade is heavily tensioned into engagement with the belt when the blade encounters even minor surface irregularities or variations in contour on the belt surface it will undesirably shift too far away from the belt. In other words, the sensitivity of the blade is not optimized in terms of its ability to stay in substantial contact with the belt surface when encountering relatively small irregularities in the surface of the belt that do not cause undue wear of the blade. Accordingly, when these irregularities are due to small pieces of material being carried back on the return run of the belt, the acutely angled blade may not be effective in scraping these off the belt surface. In such instances, it is better for the blade to stay tightly engaged with the belt for wiping the belt clean rather than to resiliently shift away therefrom. Another problem with the acute angle of the blade is that any of the blade mounts extending at the same angle will have the material scraped from the conveyor belt surface falling thereon. If this material build-up increases, it can impair the ability of the scraper blade to effectively clean the belt surface.
For resiliently urging the scraper blades into engagement with the belts, the blade mounts can have pivot biasing mechanisms associated therewith. Generally, these biasing mechanisms have been characterized by their complexity in an effort to enhance cleaning efficiency while reducing blade wear. Particularly, the pivot biasing mechanisms typically employ several pivots and linkages between the conveyor frame and the blade, as well as separate springs such that there are several components which makes these systems more susceptible to wear and failure, see e.g. U.S. Pat. No. 3,952,863 to Schattauer.
Cleaning systems are also known that employ resilient bodies such as of polymeric or elastomeric material as the primary mechanism to resiliently hold the blade in tight engagement with the belt. These types of conveyor systems generally will not be effective in high temperature conditions where the material that is being conveyed and/or the surrounding environment can be at elevated temperatures, such as conveyor belts running at asphalt and cement facilities. In high temperatures, e.g. above 180xc2x0 Fahrenheit, the polymeric or elastomeric materials can degrade so that the biasing force provided by these bodies dissipates rapidly over time. To this end, material creep for these materials can become a serious problem particularly in high temperature environments where creep can be accelerated. Likewise, the ability of polymeric or elastomeric creep materials undergoing accelerated creep to apply the same bias force to the blade over time will be compromised, as they may lose their ability to return to their original, relaxed configuration with excessive applied stress over long time durations.
Accordingly, there is a need for a conveyor belt cleaner that is better optimized in terms of its cleaning efficiency and the wear resistance of its cleaning blade. Further, a less complex mount for a cleaning blade is needed. A conveyor cleaner system that can be used in high temperature environments would also be desirable.
In accordance with the present invention, a cleaner for a conveyor belt is provided having a blade mount member for resiliently keeping a scraper blade in engagement against the belt. The blade mount member has a layback portion and a lower arcuate portion. The layback portion has the scraper blade secured to an upper end thereof and extends at a layback angle toward the belt with the lower arcuate portion spaced upstream of the upper end of the layback portion. The lower arcuate portion flexes during conveyor belt operations for controlled deflection of the layback portion that reduces loading thereon and substantially keeps the scraper blade engaged against the belt.
The use of a layback portion and a lower arcuate portion of the blade mount member presents several advantages for the present blade mount. In one aspect, the arcuate portion of the blade mount has a predetermined radius of curvature that decreases when flexed, which causes the layback portion to shift away from the conveyor belt. Thus, the displacement of the layback portion is not reflected in a corresponding amount of displacement of the flexible arcuate portion, reducing the stress in the blade mount. In other words, the flexible arcuate portion of the mount member avoids a static pivot point for the blade mount with the consequent highly localized stresses thereat, as instead, the radius of curvature of the arcuate portion changes and is reduced when the blade is loaded during its scraping engagement with the running conveyor belt. This effect is further enhanced by the relatively long length of the layback portion or arm of the blade mount member so that small decreases in the radius of the arcuate portion allow the blade to deflect sufficiently to reduce the force of high impact loads thereagainst.
Having the blade secured to the upper end of the layback portion or arm of the blade mount member allows it to more easily shift away from the belt, especially in the preferred form where the blade extends toward the belt with the same layback angle relative to the horizontal as the layback arm. As the blade is deflected, it simultaneously shifts both rearwardly or horizontally and downwardly or vertically due to the configuration of the blade mount member having the arcuate portion spaced upstream from the upper end of the layback portion and the blade thereat. For controlling this displacement of the blade, the radius of curvature of the arcuate portion is larger than the thickness of the arcuate and layback portions. Preferably, the radius is approximately two to six times the thickness of these blade mount portions. In this manner, the spring stiffness of the blade mount member is sufficiently robust to maintain good blade-to-belt contact with the sizing of the layback arm minimizing excessive wear on the blade, even in abusive applications.
More particularly, in use the layback arm portion is spring loaded with a predetermined bias force. When the blade is tensioned into engagement with the belt, the arm pivots back so that the layback angle will decrease from its size when the blade mount is relaxed. In one form, each degree of decrease of the layback angle increases the spring load of the layback arm by on average approximately eight pounds of force. For example, tensioning the blade into the belt can cause a decrease of approximately five degrees in the layback angle of the arm in its non-pivoted or relaxed configuration so that the arm and blade attached thereto are spring loaded with approximately forty pounds of force into engagement with the belt. Accordingly, as the blade undergoes normal wear, the spring load or bias force of the blade mount member keeps the blade biased into engagement with the belt surface as the layback angle can still increase back toward the relaxed layback angle of the mount while still maintaining a bias force on the blade to keep it in conformance with the belt surface.
In accordance with another form of the invention, a conveyor belt cleaning assembly is provided which includes a resilient blade mount. The blade mount preferably is of a shape-retentive metal material and secured to a rigid support of a frame for the conveyor belt. The blade mount is configured for resiliently biasing the scraper blade into engagement with the conveyor belt running in high temperature environments. As such, the cleaning assembly includes a blade mount with a minimal number of components and avoids the use of resilient bodies such as of polymeric or elastomeric materials that serve as the primary biasing mechanism for urging the scraper blade into engagement with the belts. In this manner, the cleaning assembly is well-adapted for use in harsh applications, and particularly where high temperature conditions are prevalent. In high temperatures, the metal blade mount herein retains its ability to return to its original, relaxed configuration prior to that taken when biasing the blade into engagement with the belt despite exposure to high stresses over long time durations. To this end, in contrast to polymeric/elastomeric material the present metal blade mount does not experience material creep or stress relaxation problems that can adversely affect its ability to be shape-retentive. In other words, even with the blade biased or tensioned into the belt such that the blade mount is loaded as by deflection of the layback arm, the metal material of the mount will keep substantially the same bias force on the blade despite the stresses to which it is subjected.
More specifically, the metal blade mount preferably is of a unitary, angled spring plate construction. In one form, the blade mount includes a layback portion that extends toward the conveyor belt and a base portion that extends at a layback angle to the layback portion. The layback angle is predetermined so as to minimize material build-up on the layback portion, e.g. in a range between approximately 30 degrees and up to approximately 85 degrees, and most preferably approximately 60 degrees. As mentioned, once the blade is tensioned into engagement with the belt, the layback angle will decrease with the deflected mount then providing the blade a resilient bias force that stays substantially constant during belt operations, albeit undergoing fluctuations due to deflection of the arm and consequent changing of the angle when the blade encounters surface irregularities on the belt.
Resilient material can be provided between the metal blade mount and the support for cushioning the blade during conveyor belt operations. The resilient material is preferably selected to be resistant to degradation at temperatures up to approximately 450xc2x0 F.
In an alternative, the layback portion can include an upper or upturned end portion at the upper end thereof to which the scraper blade is secured. The upturned end portion extends normal to the conveyor belt for providing the scraper blade with an optimized angle of contact with the belt.